1. Field of the Invention
The invention relates to conveyor ovens and, more particularly, to ovens in which a plate or the like is baked by directing hot air downwardly onto the upper surface of the plate from above so as to heat the upper surface of the plate uniformly. The invention is particularly useful as a pre-bake oven in a print plate imaging and processing system. The invention additionally relates to a method of using a pre-bake oven.
2. Discussion of the Related Art
So-called conveyor ovens are well known for baking plates and other relatively flat articles. Conveyor ovens are characterized by an oven having an opening through which a conveyor extends. The conveyor transports the article to be baked through the oven at a designated rate such that the article is heated to a desired temperature as it is conveyed through the oven. Conveyor ovens are used in a variety of applications.
For example, in direct print plate imaging and processing systems, conveyor ovens are used to heat print plates prior to development in order to render the background areas of the image soluble in the downstream alkaline developer of the system while simultaneously rendering the image areas insoluble. Precise and consistent heating of the print plate is essential. If the pre-baking or pre-heating step results in more than about a 2.degree. C. temperature variation across the print plate's surface, adverse effects will occur. For instance, if any portions of the plate are overheated, a thermal fog, having an appearance similar to so-called "light fog" found in conventional plates, will form in the overheated areas. Conversely, if uneven or imprecise heating leads to unacceptably low temperatures on portions of the plate, polymers in the portions of the plate which are insufficiently heated will fail to cross-link sufficiently, resulting in a weakened or removed image. Many conveyor ovens which were heretofore available did not provide adequate precision and uniformity of heating to operate acceptably as pre-bake ovens.
Conveyor ovens are also widely used in other applications such as post-bake ovens in print plate imaging and finishing systems. One such oven is manufactured by Wisconsin Oven Corporation of East Troy, Wis. and marketed as the SPC-HTS/109 Series. This oven works quite well as a post-bake oven but exhibits a relatively high profile because the heating elements, blower, and associated ductwork are all located above the conveyor. In addition, the configuration of the ductwork linking the heat source to the conveyor is less than optimal for height minimization purposes. As a result, this oven and others of its type have an overall height on the order of 74" or more. The relatively high profiles exhibited by these ovens render them somewhat unattractive in applications in which space constraints mandate ovens having the lowest-possible profile.
Many conveyor ovens which were heretofore available also were somewhat inefficient because they employed little or no air recirculation such that all or at least a substantial portion of the air used to bake the subject article was heated from ambient temperature to the working temperature.